This invention relates to a method of and apparatus for manufacturing an eyeless suture needle.
Instead of martensite-type stainless steel, austenite-type stainless steel has increasingly been used as a needle material for eyeless suture needles. Examples of such austenite-type stainless steel includes SUS304, SUS302 and SUS63151. Unlike martensite-type stainless steel, austenite-type stainless steel can not be hardened by quench hardening, and is usually hardened by work-hardening. Therefore, a wire material is cold-drawn and is hardened, and then is cut to produce needle materials. Subsequent steps are to point a distal end of the needle material, to form a mounting hole in a proximal end portion of the needle material, to insert a gut into the mounting hole and then to deform the proximal end portion of the needle material under pressure to fixedly secure the gut to the needle material, and to bend the needle material.
In order to deform the proximal end portion of the needle material to secure the gut to the needle material, the proximal end portion of the needle material is required to have a low hardness. If the hardness of the proximal end portion is high, the deformation of the proximal end portion can not be carried out satisfactorily. This may result in an unsatisfactory fixing of the gut to the needle material, and also may result in a situation in which part of the deformed proximal end portion is projected outwardly of the outer peripheral surface of the remainder, thereby adversely affecting the ability of the resultant suture needle to penetrate.
The needle material made of the austenite-type stainless steel is obliged to have a high hardness at the first stage as described above, and therefore it is necessary to sufficiently lower the hardness of the proximal end portion of the needle material by changing the crystals of the proximal end portion from a fiber-like elongated shape into a grain (particle)-like shape by means of annealing of the proximal end portion.
Japanese Utility Model Publication No. 25219/85 discloses a method in which an energy beam is applied to a needle material with its optical axis aligned with the axis of the needle material, thereby forming a mounting hole in the needle material, and thereafter a proximal end portion of the needle material is annealed using a burner. More specifically, a flame of the burner is applied to the outer peripheral surface of the proximal end portion of the needle material in a direction perpendicular or oblique to the axis of the needle material.
With this conventional method, however, the flame of the burner is unstable, and therefore there is a possibility that a very hard portion may remain at the proximal end portion of the needle material, in which case the proximal end portion can not be satisfactorily deformed under pressure. In order to avoid such disadvantage to sufficiently lower the hardness of the proximal end portion of the need material, the flame must be excessively applied to the outer peripheral surface of the proximal end portion of the needle material. As a result, the outer peripheral surface of the proximal end portion is roughened because of a local fusion thereof, and an oxide film is formed on this outer peripheral surface. Therefore, the needle material must be subjected to electropolishing for a long time, which results in a problem that the pointed distal end becomes dull, thus adversely affecting the penetrating ability of the needle.
Another problem of this conventional method is that the hardness of the needle material may be lowered over a region or length generally equal to or greater than the depth of the mounting hole. In other words, the portion of low hardness becomes excessively longer. This results in decrease of the strength of the proximal end portion of the needle material.
Japanese Patent Publication No. 55410/88 also discloses a method in which a flame of a burner is applied to a proximal end portion of a needle material in a direction perpendicular to the axis of the needle material, thereby annealing this proximal end portion.
U.S. Pat. No. 4,910,377 discloses a technique in which a mounting hole is formed in a proximal end portion of a needle material by an energy beam such as a laser beam and an electron beam.
Japanese Laid-Open (Kokai) Utility Model Application No. 43691/80 and Japanese Laid-Open Patent Application No. 184485/85 disclose a technique in which when forming a mounting hole in a proximal end portion of a needle material, the focus of a condenser lens is spaced or displaced from the proximal end portion of the needle material.
Japanese Laid-Open Patent Application No. 110532/84 discloses a device for supporting needle materials. This device comprises a rotary disk having V-shaped grooves, and a holder member.
U.S. Pat. No. 4,935,029 discloses a technique in which a needle material and a pipe material are welded together by an energy beam, and subsequently the welded portion, as well as the pipe material if necessary, is annealed by an energy beam. In this annealing method, however, the energy beam is applied in a direction perpendicular to the axis of the needle material, and the needle material is not only moved in its axial direction but also is rotated. In this method, the time required for the annealing is very long.